A tidy village dedicated to the future of green, solar-powered living has taken over the heart of the National Mall, where 20 teams of college students are vying to see who can build the most appealing energy-efficient home.

The teams, from universities in North America and Europe, are competing in the Department of Energy's biennial Solar Decathlon, which runs through next weekend. The challenge: design and build a prototype house that can provide the comforts of home while generating all the energy residents need from the sun's rays. Teams get bonus points if they can produce surplus electricity and sell it back to the power company.

The transformation began at 11 p.m. on Sept. 30, when the first flatbed trucks carrying building modules were allowed to roll onto the Mall between the Smithsonian Castle and 14th Street NW. Student-led teams, backed by professional builders, suppliers and advisers, turned the Mall into a feverish construction site from early morning until late each evening, readying the houses for the opening ceremony Thursday. They built sleek pyramids, rusty silos, reclaimed-water gardens, glassy boxes and shaded porches. And each house sports an electric meter that can run in reverse, giving the team credit for each kilowatt it can sell into Pepco's electric grid.

The avant-garde neighborhood is open for free tours daily through Oct. 18, except for Wednesday, when the houses are closed for judging.

A decathlon, of course, consists of 10 events. These houses are being judged for their architecture, market viability, engineering, comfortable temperature and humidity, hot water production, appliances, entertainment, communication with the public, lighting design, and ability to produce at least as much energy as they consume.

The competition is designed to push solar technology forward -- and to train the next generation of architects, engineers and other design pros to create homes that operate with nearly no carbon footprint, according to Richard J. King, who runs the project for the Energy Department.

"We don't know how to do it in the United States; otherwise we'd have solar houses all over the place," he said. In the past three decathlons, students have learned from their competitors and incorporated winning ideas into subsequent designs. "They learn from each other; they learn what really works," he said. "It's a wonderful iterative process of advancement."

He noted that several teams that competed in past decathlons have gone on to form their own energy technology companies. And some technologies used in previous entries, such as structural beams made of fast-growing bamboo, are already starting to be commercialized.

This year's contestants, chosen a year ago from 40 entries, were each awarded $100,000 from the Department of Energy to build the prototypes. That funding was supplemented by team fundraising and corporate sponsorships. From this point on, the teams are competing simply for bragging rights.

The teams have taken wildly different approaches to their designs. Some reflect how environmental conditions differ from Ontario to Arizona. But others reflect the teams' distinct priorities. Several focus on cutting-edge technology, while others have tried to take off-the-shelf technology and produce a home that could be taken to the mass market quickly and affordably.

One example of the cutting-edge approach would be Team Spain's entry, built by Universidad Politécnica de Madrid. Unabashedly modern, the house sits under a large inverted pyramid that contains solar-electric panels and solar-heating water collectors. The pyramid is attached to the roof with a ball-and-socket mechanism that pivots the pyramid to track the sun. The sides of the pyramid also reflect sunlight into the house through skylights.

Virginia Tech's house incorporates sliding-glass walls on the north and south faces. The walls can be opened and closed automatically by an in-house computer linked to indoor climate sensors and an outdoor weather station. The walls can also be operated by iPhone.